Catalytic production of hydrocyanic acid



May 8, 1934. L. ANDRussow Er AL CATALYTIC PRODUCTION OF HYDROCYANIC ACID Filed D60. 14, 1931 TORS Patented May 8, 1934 UNITED STATES PATENT omer.:

'KCATALYTIC PRODUCTION 0F HYDRO- CYANIC ACID Application December 14, 1931, SerialNo. 580,866

In Germany December 19, 1930 (Cl- 23-15l) 7 maints.

The present invention relates to improvements in `and apparatus for carrying out the catalytic production of hydrocyanic acid.

In the preparation of hydrocyanic acid from fr, gas mixtures comprising ammonia, at least one vaporizable hydrocarbon and a gas comprising oxygen, such as ain in the presence of metallic catalysts, such as platinum, iridium, ruthenium, palladium, osmium, gold or alloys of these metals l@ or alloys of metals or the iron group, such as of nickel and chromium, which catalysts may be present in the form of netting, wire gauze, chips, balls or the like, as for example according to the process or" application Ser. No. 528,239 iiled by the 3g irst of the above mentioned inventors, deposition or" carbon and corrosion of the catalyst often takes piace at places where the catalyst and reaction vessel touch or are near to each other.

We have now found that this objection is almost g@ entirely avoided by rinsing the said endangered places withv gases which contain practically no constituents which form carbon black at the temperatures prevailing in the said reaction and which in particular are free from hydrocarbons. 2g In the said reaction carbon may be deposited on the edges oi` the netting after some period of working and this may lead to a gradual destruction or" the edges of the netting. At the same time 'the yield of hydrocyanic acid becomes increas- 3@ ingly smaller. If a rinsing gas be led through one or more small slots at those places in the walls oi the vessel to which the edges of the netting are clamped for the purpose of fixing them, no carbon is deposited and there yis no corrosion of the catalyst even after Working for long periods of time. By appropriately arranging and shaping the slots, a very small amount of rinsing gas, as for example less than l per cent of the reaction gases employed, is sufficient.

In many cases it is advantageous to employ a rinsing gas containing small amounts of o'xy'gen. The rinsing gas may contain up to 4 per cent of oxygen, for example, without the yield of hydrocyanic acid being injuriously affected. The presence of oxygen in the rinsing gas renders it possible to use a comparatively small amount of the latter. In particular, the oxygen has the effect of" removing any nucleus of carbon black previously formed. The oxygen may, if desired, also be employed in a combined form, especially in the form of steam or carbon dioxide.

It is of particular advantage to employ as rinsing gases pure nitrogen or the nitrogen obtained by liquefaction of air in the so-called Linde p5 process. Also industrial gases containing a substantial amount oi nitrogen, such as waste combustion gases or the waste gases from the aforesaid preparation of hydrocyanic acid may be employed. If these industrial gases contain carbon monoxide or hydrocarbons or other substances capable of forming carbon under the working conditions these substances are previously converted into carbon dioxide which may be eected for example by passing the said waste gases at high temperatures over reducible metal oxides or by combustion with an appropriate amount of air.

If the presence of carbon dioxide is not desired, for example when hydrocyanic acid formed is to be subsequently absorbed by alkalies, the carbon dioxide contained in the gases to be used for rinsing purposes may previously be removed therefrom by the usual methods.

In order to reduce or prevent cooling of the catalyst at the places where the rinsing gases enter, it is preferable to preheat the rinsing gases. This is especially the case when the formation of carbon black for example by higher hydrocarbons lsuch as oilgas or cracking gases is promoted by a reduction in the temperature.

An eicient rinsing may be eiected in various 30 ways. When employing catalysts in the form of netting, it may be elected in a particularly simple manner.

One method of effecting the said rinsing when employing a catalyst in the form of netting will be described with reference to the accompanying drawing, but the invention is not restricted to this yparticular method or to the particular arrangement shown.

Two rings R1 and Rz of ceramic material are 90 so spaced in a cylindrical reaction vessel G by means of packing D that between them and the wall of the vessel there is a small annular hollow space H. The netting N is situated between the two rings R1 and R2. A rinsing gas enters through 95 a pipe O into the hollow space H, is preheated therein and then passes through the clamping joint F and the edge of the netting N into the reaction vessel. i

Inf some cases, in particular when operating incomparatively wide tubes having a diameter of more than 20 cms., it is of advantage to place the'catalytic nets loosely and while avoiding tensions on metallic gratings composed of wires or bars and to pass the reaction gases downwardly. 10?

4If the nets are` rmly attached to the gratings,

for example by welding, tensions may be caused due to the difference of thermal expansion of the nets and the gratings, which tensions readily lead to ruptures. It is preferable not to employ 110 gratings the bars of which are excessively large in comparison with the meshes of the catalytic nets, since at the places where the finely meshed net touches the thick bars of the gratings the passage of the reaction gas is4 hindered whereby the carbonaceous compounds contained in the said gases are readily decomposed with the formation of carbon. The stoppage of the reaction gases may, however, be diminished by imparting to the said bars an appropriate shape, for example by providing that the circumference of the cross-sectional area of the bars has the form of a stream-line. Gratings of ceramic materials are less suitable than gratings made of metals or alloys; of the latter noble metals and their a1- loys, or alloys of the iron group, such as chromium-nickel or other high melting metals or alloys are of advantage.

The reaction according to the present invention is effected at temperatures ranging between 700 and 1250 C., preferably between 800 and 1150 C. Subatmospheric,l ordinary and superatmospheric pressures may be employed; in practice ordinary pressures are preferred.

The nature of the present invention will be further understood by the following examples; the invention is, however, not restricted to these examples.

Example 1 A gaseous mixture containing 11.1 per cent by volume of ammonia, 12'per cent of crude methane in the form of natural gas, 15 per cent of oxygen, 0.8 per cent of hydrogen and 61.1 per cent of nitrogen is passed at a velocity of ilow of 30 cubic metres (of the gas under normal pressure and at a temperature of 15 C.) per hour and at a temperature of from 980 to 1050 C. through three joint nets which consist of platinum containing 10 per cent of rhodium and which have 1024 meshes per square centimetre. The said nets are arranged in a tube, 10 centimetres in internal diameter, in a manner equal or similar to that shown in the accompanying drawing. Nitrogen is supplied in an amount of about 0.8 cubic metre per hour to the places at which the nets come into contact with, or are near to, the walls of the said tube. About two-thirds of the ammonia employed are converted into hydrocyanic acid while the rest remains substantially unaltered. The corrosion of the catalytic nets soon taking place without the use of rinsing gases cannot be observed even after 6 weeks when working in the aforedescribed manner.

Example 2 A gas mixture consisting of 11 per cent by volume of ammonia, 12 per cent of methane, 15.6 per cent of oxygen and 61.4 per cent, of nitrogen is passed downwardly in a tube 25 centimetres in internal diameter which is constructed of a ceramic material and which is of the kind shown in the accompanying drawing. As catalysts serve two joint nets each having 1024 meshes per square centimetrev and which consist of a wire, 0.06 millimetre in thickness, of an alloy of platinum containing 15 per cent of rhodium. The'said nets are loosely placed on a grating the bars of which consisting of the same material are 0.5 millimetre thick and 10 millimetres distant from each other. The gratings may also be made of another metallic material as for example .an alloy of chromium and nickel. The nets and the grating are clamped in the aforedescribed' manner between two rings of a ceramic material. The rinsing of places at which the nets are clamped is effected by means of nitrogen containing 2 per cent of oxygen and which is supplied in an amount of 2 cubic metres per hour. The temperature at the netsamounts to about 1000 C. By passing the reacting gases through the nets at a velocity of 160 cubic metres (of the gases under normal pressure and at a temperature of 15 C.) per hour 312 kilograms of hydrocyanic acid are obtained in a course of 24 hours. -After using the nets for about 2 months they are only negligibly corroded and may be employed for longer periods.

What we claim isz- 1. In the production of hydrocyanic acid by interaction of ammonia, a vaporizable hydrocarbon and a gas comprising free oxygen, at a temperature between 750 and 1250 C. and in the presence of a metallic catalyst, the step which comprises rinsing during the reaction the places at which the said catalyst comes into contact with the reaction vessel with a gas free from constituents depositing carbon at the said temperature.

2. In the production of hydrocyanic acid by interaction of ammonia, a vaporizable hydrocarbon and a gas comprising free oxygen at a temperature between 750 and 1250 C. and in the presence of a catalyst comprising a free metal of the eighth group of the periodic system and having an atomic number between 44 and 78, the step which comprises rinsing during the reaction the places at which the said catalyst cornes into contact with the reaction vessel with a gas free from constituents depositing carbon at the said temperature.

'3. In the production of hydrocyanic acid by interaction of ammonia, a vaporizable hydrocarbon and air at a temperature between 750 and 1250 C. and in the presence of a metallic catalyst, the step which comprises rinsing during the reaction the places at which the said catalyst comes into contact with the reaction vessel with a gas free from constituents depositing carbon at the said temperature.

4. In the production of hydrocyanic acid by interaction of ammonia, a vaporizable hydrocarbon and a gas comprising free oxygen at a temperature between 750 and 1250 C. and in the presence of a metallic catalyst, the step which comprises rinsing during the reaction the places at which the said catalyst comes into contact with the reaction vessel and those which are near those places with a gas free from constituents depositing carbon .at the said temperature.

5. In the production of hydrocyanic acid by interaction of ammonia, a vaporizable hydrocarbon and air at a temperature between 750 and 1250 C. and in the presence of a metallic catalyst, the step which comprises rinsing during the reaction the places at which the said catalyst comes periodic system and having an atomic number between 44 and '78, the step which comprises rinsing during the reaction the places at which the said catalyst comes into contact with the reaction vessel with nitrogen containing oxygen.

LEONID ANDRUSSOW. KARL HUBERICH. 

